Ion chromatography is a known technique for the analysis of ions which typically includes a chromatographic separation stage using an eluent containing an electrolyte, and an eluent suppression stage, followed by detection, typically by an electrical conductivity detector. In the chromatographic separation stage, ions of an injected sample are eluted through a separation column using an electrolyte as the eluent. In the suppression stage, electrical conductivity of the electrolyte is suppressed but not that of the separated ions so that the latter may be determined by a conductivity cell. This technique is described in detail in U.S. Pat. Nos. 3,897,213, 3,920,397, 3,925,019 and 3,926,559.
Among the many applications for ion chromatography, a significant application of ion chromatography is in analyzing water, e.g., surface water and well water. Worldwide, municipal facilities use ion chromatography to qualify water as being appropriate for human consumption. The ionic content of water varies significantly depending on the source, storage and handling conditions. In samples containing high levels of matrix ions such as chloride, sulfate and bicarbonate detecting trace amounts of ions such as bromate or chlorite or perchlorate is challenging.
Methods for ion analysis of water include direct injection and analysis, or pretreating the samples prior to a direct injection analysis. Direct injection is preferred, however, application of this method is limited for some samples with high matrix content due to the limited capacity of the stationary phases currently available. An alternate approach is to pursue pre-concentration of the ions in the sample in conjunction with heart cutting or some means of removing the matrix ions prior to analysis. Heart cutting methods are two-dimensional methods in which the matrix ions are separated or removed in the first dimension, enabling analysis of the ions of interest. Matrix ions are also removed using sample pretreatment with one or more pretreatment cartridges. For example a barium form cation exchange resin based cartridge is used to remove sulfate from the sample matrix. The methods discussed above are multi-step processes with multiple valve configurations, complex plumbing or are labor intensive. Therefore it is desirable to simplify the analysis protocol for samples containing matrix ions. Ion exchange phases having unique enhanced capacity architecture will facilitate analysis.
To counter some of the limitations of existing stationary phases a new phase and method of making this phase was recently introduced (U.S. Pat. No. 7,291,395). The method and phase rely on an amine epoxide-based chemistry to grow a hydrophilic hyperbranched structure on top of the substrate of the ion exchange phase. This type of structure does not have the limitation of inter-penetrating polymers of the prior art phases and shows excellent efficiencies. The capacity of these phases, however, could be enhanced to facilitate direct injection of samples with high matrix ion concentration.
Ion exchange phases should provide high resolution of species of interest, particularly over matrix ions, and the ability to handle high matrix ion concentrations without over-loading the stationary phase. These phases should also allow quantitation at trace levels of ions other than matrix ions and have unique selectivity to facilitate separation of species of interest. Furthermore, a desirable ion exchange material will be resistant to binding matrix ions, preventing these ions from interacting with the stationary phase and decreasing available capacity of this phase. The present invention provides such high capacity stationary phases and methods of making and using them.